Since the discovery of natural hydrocarbon hydrates in subterranean geological formations, several approaches have been developed for releasing and collecting the hydrocarbon gas as an energy resource. One particular approach comprises replacing the hydrocarbon hydrate by carbon dioxide hydrate, which is expected to have advantages in terms of dumping carbon dioxide simultaneously with the collection of hydrocarbon gases. Several techniques for converting hydrocarbon into carbon dioxide hydrates have been proposed in the past.
Injecting liquid carbon dioxide into a gas hydrate formation has been proposed in U.S. Pat. No. 5,261,490 A (1993) and in JP 06-071161 (1994). With these techniques, it has been proposed to heat the gas hydrate with the liquid carbon dioxide resulting in melting the gas hydrate and a carbon dioxide hydrate formation. Disadvantages of this concept result from an uncontrolled melting of the gas hydrate, which may lead to an instability of the geological formation. Furthermore, the released hydrocarbon still includes large amounts of carbon dioxide, which have to be separated from the hydrocarbon gas and re-processed.
Further thermodynamic investigations of carbon dioxide and hydrocarbon gas hydrates have been described by B. Kvamme et al. (“J. Phys. Chem.”, volume 99, 1995, p. 7114-7119) and by S. Hirohama et al. (“Journal of chemical engineering of Japan”, volume 29, 1996, p. 1014-1020). S. Nakano et al. (“Proc. Instn. Mech. Engrs.”, volume 212 A, 1998, p. 159-163) have described that the carbon dioxide hydrate formation is an exothermic reaction, which would heat the hydrocarbon hydrate. S. Hirohama et al. and S. Nakano et al. have introduced models of hydrate conversion, wherein a conversion rate is limited entirely by heat transport and corresponding enthalpy changes. On the contrary, B. Kvamme et al. have disclosed a differentiated model distinguishing process wherein the conversion rate is kinetically limited by the phase transition itself through Gibbs free energy differences or by mass and heat transport alone. While the theoretical conversion of the hydrocarbon to the carbon dioxide hydrate has been confirmed in these publications, practical implementations for processing geological hydrocarbon hydrates have not been investigated or proposed.
Another technique for injecting carbon dioxide and replacing methane in gas hydrates is described in US 2006/0060356 A1. A solid state conversion is described, wherein methane is replaced exclusively using the fact that carbon dioxide hydrate has a larger thermodynamic stability compared with methane hydrate. This conversion process is dominated by a solid state diffusion process, which may represent disadvantages in terms of a low conversion rate and low conversion efficiency. Another disadvantage may result from the fact that practical geological systems include mineral components, which may deteriorate the solid state conversion.
It is desirable to provide an improved method of creating a carbon dioxide hydrate, which method is capable of avoiding disadvantages of conventional techniques and which in particular is capable of replacing a hydrocarbon hydrate by a carbon dioxide hydrate with an increased reaction rate and an improved conversion efficiency. It also is desirable to provide an improved method of releasing a hydrocarbon gas from a subterranean geological formation. Such a method should be implemented in a controlled manner without destabilizing the geological formation. It would also be desirable to provide an improved substance composition, which facilitates the formation of a carbon dioxide hydrate in a subterranean geological formation. Still further, an improved deposition device for depositing carbon dioxide hydrate in a subterranean geological formation is desirable, which is capable of avoiding disadvantages of the conventional techniques and which is compatible with conventional borehole techniques and deposition devices.